How to model an air mattress?
You could begin this way:

Create a plane, rotate it 45° on the Z axis, cut 2 obliques:



Bevel, extrude up, delete the bottom, mirror, extrude the joints:





Give it an Array modifier on the X axis, enable its Merge option:



Give it a second Array so that it duplicates the row on the Y axis:



And then a third Array, on the Y axis again, that duplicates the first two rows:



Give it a Subdivision Surface modifier, play with the Array modifiers &gt; Merge &gt; Distance value so that the vertices stick to each others...